The invention relates to a magnetic head for use with a tape recorder or the like.
A conventional monoaural magnetic head is shown in FIG. 1, in which a pair of symmetrical core pieces 1, 2 of a ferromagnetic material define a gap 3 by interposing a material such as ceramic therebetween. The assembly is enclosed by left- and right-hand non-magnetic blocks 4, 5 and by upper and lower non-magnetic blocks 6, 7, all of which are molded from a synthetic resin adhesive material. The rear portion is covered by a non-magnetic block 8, with a pair of terminal members 9, 10, which are connected with a coil disposed on the core pieces 1, 2, extending through the rear portion. An example of head which may be used for stereophonic applications is illustrated in FIG. 2 wherein it will be noted that an additional pair of core pieces 12, 13 which defines another gap 14 are juxtaposed with the first mentioned pair of core pieces 1, 2 with a shield plate 11 interposed between the respective pairs. Another pair of coil terminals 15, 16 is associated with the core pieces 12, 13.
When manufacturing such a conventional magnetic head, the monoaural head shown in FIG. 1 is usually formed by disposing the non-magnetic blocks 4 to 8 around the core pieces 1, 2 (see FIG. 3) and filling the spaces between the core pieces 1, 2 and the respective non-magnetic blocks 4 to 8 with a synthetic resin adhesive, which is molded into a layer 17. At this end, it is necessary to provide a track width Wa for the core pieces 1, 2 which is different from the width Wb of the non-magnetic blocks 4, 5 for the sake of the thickness of the layer 17. In other words, the different values of the widths Wa, Wb resulted from the manufacturing requirements for providing the layer 17. The same applies to the manufacturing of a stereophonic magnetic head shown in FIG. 2. The same is also true where the non-magnetic blocks 4, 5 and 6 are formed integrally to provide a non-magnetic body 18 as shown in FIG. 4 or where all of the non-magnetic blocks 4 to 7 form one intergral unit to provide a non-magnetic body 19 as shown in FIG. 5.
In these conventional magnetic heads, since the layer 17 is much softer than the material of the core pieces, fine particles of the magnetic material which are produced by the frictional engagement between the core pieces and the tape tend to be trapped by the layer 17, thereby considerably degrading the performance of the magnetic head. The situation is similar in a composite head as shown in FIG. 6 in which an erase head and a record/playback head are integrally unified.
In a conventional composite head, the track width of an erase gap is greater than the track width of a record/playback gap. This is because of the fact that when recording a magnetic tape, it tends to oscillate crosswise during its running, though slightly, to cause a tortuous recording track which can only be completely erased by providing an increased width for the erase gap.
FIG. 6 shows an example of such a composite magnetic head. An erase gap 21 is defined between a central core piece 22 and a right-hand core piece 23 which is located at the same level as the core piece 22. A record/playback gap 24 is defined between the central core piece 22 and a left-hand core piece 25 which is reduced in elevation relative to the core piece 22. The record/playback gap 24 has a width Wc which is reduced as compared with the width Wd of the erase gap 21. For this reason, after finishing the respective core pieces 22, 23 and 25 so that their lower surfaces are flush with each other, the cores 22 and 25 are located so that their upper surfaces are offset by an amount equal to Wd - Wc, and are then secured to the inside of a shield case 27 molding of a synthetic resin adhesive 26.
The shield case 27 is fixedly mounted on a support plate 27a, and carries on its left-hand sidewall a pair of upper and lower tape guides 28a, 28b which are disposed so that a magnetic tape 29, shown in phantom lines, can be passed therebetween in sliding contact with the front surface of the composite magnetic head in a direction indicated by an arrow a, thereby permitting an erase, a record or a playback operation on a magnetic track portion of the tape which is indicated by a width We, while maintaining such portion which is located below the centerline 29a in abutment against both gaps 24 and 21.
When manufacturing such a composite magnetic head, it is necessary that the lower surfaces of the respective core pieces 22, 23 and 25 be finished so as to be flush with each other, and to determine, with a high accuracy, the difference Wd - Wc in the width of the both gaps 21, 24, and the distance Wf from the upper edge of the lower tape guide 28a to the centerline 29a of the magnetic tape 29 as well as the track width We or the distance from the upper edge of the guide 28a to the upper edge of the magnetic track. When a ferromagnetic material of an oxide type such as ferrite or the like is used for the core of the composite magnetic head, it is desirable that a non-magnetic block which has a hardness and the other mechanical properties approaching those of the ferrite be arranged around the core. However, in practice, because of the presence of the step defined by the difference Wd - Wc, this region and the remainder of the periphery had to be filled with a synthetic resin adhesive 26 which is poured therearound. This results in the formation of a depression in such region as a result of the differential hardness between the core pieces and the resin material and may disadvantageously cause an accumulation of dust therein or rubbing off the surface of the magnetic tape.
Where an alloy such as permalloy is used for the core material of the magnetic head, the entire peripheries of the respective core pieces have to be supported by core retaining blocks. However, the presence of the step Wd - Wc creates a non-uniform clearance between the core pieces and the core retaining blocks, rendering it difficult to achieve a high accuracy in locating the parts so as to produce the differential gauge Wd - Wc as well as the track width We or the above mentioned distance Wf.